g out
mixed series, the members of which change from vivid to obscure with
increase of refrangibility. It is difficult to imagine by what
chromospheric machinery this curious result can be produced. Alcyone in
the Pleiades presents the same characteristic. Alone among the hydrogen
lines, crimson C glows in its spectrum, while all the others are dark.
Luminosity of the Wolf-Rayet kind is particularly constant, both in
quantity and quality. It seems to be incapable of developing save under
galactic conditions. All the stars marked by it lie near the central
line of the Milky Way, or in the Magellanic Clouds. They tend also to
gather into groups. Circles of four degrees radius include respectively
seven in Argo, eight in Cygnus.

The first spectroscopic star catalogue was published by Dr. Vogel at
Potsdam in 1883.[1406] It included 4,051 stars, distributed over a zone
of the heavens extending from 20 deg. north to 20 deg. south of the
celestial equator.[1407] More than half of these were white stars,
while red stars with banded spectra occurred in the proportion of about
one-thirteenth of the whole. To the latter genus, M. Duner, then of Lund,
now Director of the Upsala Observatory, devoted a work of standard
authority, issued at Stockholm in 1884. This was a catalogue with
descriptive particulars of 352 stars showing banded spectra, 297 of which
belong to Secchi's third, 55 to his fourth class (Vogel's iii. _a_ and
iii. _b_). Since then discovery has progressed so rapidly, at first
through the telescopic reviews of Mr. Espin, then in the course of the
photographic survey carried on at Harvard College, that considerably over
one thousand stars are at present recognised as of the family of Betelgeux
and Mira, while about 250 have so far exhibited the spectral pattern of
19 Piscium. One fact well ascertained as regards both species is the
invariability of the type. The prismatic flutings of the one, and the
broader zones of the other, are as if stereotyped--they undergo, in
their fundamental outlines, no modification, though varying in relative
intensity from star to star. They are always accompanied by, or
superposed upon, a spectrum of dark lines, in producing which sodium and
iron have an obvious share; and certain bright rays, noticed by Secchi
with imperfect appliances as enhancing the chiaroscuro effects in
carbon-stars, came out upon plates exposed by Hale and Ellerman in 1898
with the stellar spectrograph of the Yerk